The present invention relates to a high-performance, simple-in-structure brake fluid pressure controller functioning both as an antilock controller and a traction controller.
The most cost-effective and thus most popular antilock controller type is known as a dump & pump type. This type of antilock controller has a brake fluid pressure control valve including a discharge valve and provided in a main fluid line leading from the master cylinder to the wheel brakes. While the brake pressure is being reduced in an antilock control mode, brake fluid discharged from the discharge valve is stored temporarily in a discharged fluid reservoir, and returned to the main fluid line with a pump when the brake pressure is re-increased.
If the pump for returning fluid into the main fluid line is used also to increase the brake pressure for traction control, it is possible to use this antilock controller as a traction controller as well. A controller of this type is disclosed in Unexamined Japanese Patent Publication 64-74153. It is basically a fluid-return type antilock controller with an on-off valve further added thereto. During traction control mode, the fluid supply line is connected to the main fluid line through the on-off valve, while they are disconnected from each other while no traction control is being performed. But with this arrangement, fluid has to be supplied from the master cylinder reservoir through a pipeline during traction control, so that the pump cannot draw and discharge brake fluid at a sufficiently high rate. Thus, the response was not high enough.
On the other hand, Unexamined Japanese Patent Publication 6-72301 proposes to provide a second reservoir in addition to the discharged fluid reservoir in order to supply fluid smoothly to the pump. But in this arrangement, when the pump is activated while the fluid pressure produced in the master cylinder (hereinafter referred to as master cylinder pressure) is zero, the piston in the second reservoir will move, making it impossible to supply fluid for traction control. Also, every time the brakes are applied, a piston for suppressing the activation of the second reservoir when the master cylinder pressure is produced moves in and out. This extends the brake pedal stroke. Due to these problems, this controller is practically useless.
Unexamined Japanese Patent Publication 4-231241 proposes to use an active pressure accumulator having a driving device as the abovementioned second reservoir. This accumulator operates in a desirable manner, and can supply fluid to the pump more efficiently than the reservoir without a driving device. But a considerable increase in cost due to the provision of the driving device and its driving circuit is unavoidable.
In order to solve these problems, the applicant of the present invention proposed an improved brake fluid pressure controller in Unexamined Japanese Patent Publication 5-116607.
This controller has a wheel brake fluid pressure control valve including at least a discharge valve and provided in a main fluid line leading from a master cylinder to a wheel brake, a discharged fluid reservoir for temporarily storing brake fluid discharged from the discharge valve, a pump for drawing brake fluid stored in this discharged fluid reservoir and returning it to the main fluid line at a fluid return point, a fluid supply line branching from the main fluid line at a point upstream from the fluid return point and leading to the discharged fluid reservoir, a changeover valve for preventing the flow of fluid from the fluid return point to the master cylinder during traction control mode, and a shutoff valve for preventing the flow of fluid from the fluid supply line toward the discharged fluid reservoir while the master cylinder is being pressurized, and is characterized in that an intermediate fluid reservoir is provided upstream of the shutoff valve near the master cylinder so that it communicates with the fluid supply line at least during traction control.
Unexamined Japanese Patent Publication 5-193473 also discloses a similar controller provided with an intermediate fluid reservoir in the main fluid line.
The controller we proposed in Unexamined Japanese Patent Publication 5-116607 has advantages in that fluid can be supplied smoothly into the pump by the provision of the intermediate fluid reservoir, and that the intermediate reservoir is prevented from remaining empty because it is connected with the main fluid line.
But this controller has problems in that the shutoff valve disposed between the intermediate fluid reservoir and the pump produces a force that resists the suction force of the pump, and that the provision of the shutoff valve and the intermediate reservoir complicate the structure of the entire controller. It is further necessary to provide a piston in the intermediate chamber to define an atmospheric-pressure chamber and a fluid chamber therein. The provision of the piston necessitates some measures to prevent the piston from getting locked due to rusting or icing.
An object of the present invention is to provide a high-performance, cost-effective, reliable, compact fluid-return type brake fluid pressure controller having both the functions of an antilock controller and a traction controller.